Method for the element of mercury from a feedstock downstream of a fractionation unit

ABSTRACT

Process for the elimination of mercury contained in a heavy hydrocarbon-containing feedstock downstream of a main fractionation unit, a process in which:
     a) the non-elemental mercury contained in the compounds of said feedstock is transformed to elemental mercury;   b) a fractionation of said hydrocarbon-containing feedstock is carried out in a fractionation unit in order to produce a top effluent comprising elemental mercury;   c) the top effluent obtained in stage b) is brought into contact with a mercury capture material contained in a unit for the capture of mercury, in order to obtain an effluent that is at least partially de-mercurized.

TECHNICAL FIELD

The present invention relates to a process for the elimination of heavy metals, and more particularly mercury, that are present in a liquid or gaseous feedstock.

STATE OF THE ART

Mercury is a metallic contaminant that is found in gaseous or liquid hydrocarbons produced in many regions of the world, such as the Niger Delta, South America or North Africa.

The elimination of mercury from hydrocarbon cuts is desirable in an industrial context for several reasons:

-   -   for reasons of the safety of operators: elemental mercury is         volatile and presents serious risks of neurotoxicity via         inhalation, while its organic forms present similar risks via         skin contact.     -   for reasons of preventing de-activation of the heterogeneous         catalysts serving to upgrade these liquid hydrocarbon cuts:         mercury amalgamates very readily with the noble metals such as         platinum or palladium used for various catalytic operations, and         in particular the selective hydrogenation of the olefins         produced by steam cracking or catalytic cracking of liquid         hydrocarbons.

Industrially, the elimination of heavy metals, in particular mercury, from the liquid or gaseous hydrocarbon cuts is carried out by circulating them through beds of capture material. By capture material is meant in the present invention any type of solid in bulk or supported form containing within it or on its surface an active element capable of reacting irreversibly with an impurity such as mercury contained in the feedstock to be purified. The elimination of mercury from the liquid or gaseous hydrocarbon-containing cuts is generally carried out by circulating said feedstock to be treated through beds of capture materials containing an active phase capable of reacting with the mercury. It is in particular known to a person skilled in the art that mercury capture can be carried out easily by reacting the latter with an active phase based on sulphur or a sulphur-containing compound, in particular metallic sulphides, the mercury then forming with the sulphur the chemical species HgS called cinnabar or metacinnabarite. These different chemical reactions are generally implemented in a process by using contact of the feedstock to be treated with a capture material that is either bulk in which the particular particles of the active phase can be bonded together via binders, or supported in which the active phase is dispersed within or on the surface of a porous solid support.

However, it is not possible to carry out such a purification operation directly on crude oil cuts or gas condensates for several reasons. The first is that the porosity of these capture materials would very quickly become clogged by the heavy compounds present in said feedstock, which would be deposited on the surface of the materials. Furthermore, these crude oil cuts or gas condensates contain mercury in different forms. In fact, unlike the gas phases, they contain not only elemental mercury but also mercury in complexed or ionic or even organic form. Now, these complexed or ionic and organic compounds of mercury are called refractory, as they are stable under normal operating conditions and are not reactive with the capture materials of heavy metals. It therefore appears to be necessary to convert the refractory mercury compounds to elemental mercury.

Numerous means have been developed in order to convert the refractory forms of mercury to elemental mercury (also called mercury in atomic form Hg⁰). For example, U.S. Pat. No. 4,911,825 discloses a process for the transformation of the refractive species of mercury from the feedstock to elemental mercury in the presence of a catalyst and under high hydrogen pressure and at a high temperature.

U.S. Pat. No. 5,384,040 discloses a process for the elimination of the mercury from a hydrocarbon-containing feedstock comprising a stage of transformation of the mercury contained in the compounds of the feedstock to elemental mercury, the transformation stage being carried out between 120 and 400° C. and under pressure of 0.1 to 6.0 MPa. Preferably, the transformation stage is carried out in the presence of a catalyst comprising at least one metal M selected from the group formed by iron, nickel, cobalt, molybdenum, tungsten and palladium.

Alternatively, the transformation stage can be carried out in the absence of a catalyst. In the latter case, the temperature must be set at a minimum of 180° C. In fact, in the article by Masatoshi Yamada et al. entitled “Mercury removal from natural gas condensate” in the journal Studies in Surface Science and Catalysis, volume 92, pages 433-436, 1995, it is shown that the conversion of diethyl mercury starts at 180° C. and reaches 100% conversion at 240° C. At the same time, it is shown that it is possible to reduce the transformation temperature in the presence of a catalyst. In fact, the conversion of the refractory species of mercury starts at 130° C. and reaches over 90% from 200° C. However, the problem with the use of a catalyst, apart from its cost, is that there is a tendency to promote the cracking of molecules and therefore the formation of coke. Furthermore, in the case of highly clogging feedstocks such as crude oil, a very rapid de-activation of the porous catalyst is noted, due to the deposition of heavy compounds such as asphaltenes, within the pores of said catalyst. Such a process is thus more suitable for the treatment of hydrocarbons originating from a first fractionation.

The Applicant discovered, surprisingly, that it is possible to efficiently eliminate heavy metals, and more particularly mercury, contained in a gaseous or liquid feedstock, and more particularly a crude oil feedstock, by carrying out upstream of the main fractionation unit, a stage of heating said feedstock at a target temperature and during a residence time sufficient to allow the conversion of the heavy metals, present in different forms, to metals in the atomic (or elemental) form, even without the use of any catalytic treatment or under hydrogen, and by carrying out immediately downstream of the main fractionation unit, a stage of capture of the heavy metals, and more particularly mercury. In fact, although the crude oil feedstocks comprise a very great diversity of molecules, bringing said feedstock up to a temperature during a sufficient residence time upstream of the main fractionation unit makes it possible to convert the majority of the refractory compounds to metallic compounds that can be captured by a single capture material situated immediately downstream of the main fractionation unit.

SUBJECTS OF THE INVENTION

The present invention relates to a process for the elimination of mercury contained in a heavy hydrocarbon-containing feedstock downstream of a main fractionation unit, a process in which:

a) the non-elemental mercury contained in the compounds of said feedstock is transformed to elemental mercury, said stage being carried out in a conversion unit at a target temperature during a fixed residence time and adapted to said target temperature so that at least 90% by weight of non-elemental mercury contained in the compounds of said feedstock is converted to elemental mercury, said stage of transformation being carried out in the absence of hydrogen and in the absence of a catalyst, it being understood that:

-   -   when the target temperature of said feedstock is comprised         between 150° C. and 175° C., the residence time of said         feedstock in the conversion unit is comprised between 150 and         2700 minutes; and/or     -   when the target temperature of said feedstock is greater than         175° C. and less than or equal to 250° C., the residence time of         said feedstock in the conversion unit is comprised between 100         and 900 minutes; and/or     -   when the target temperature of said feedstock is greater than         250° C. and less than or equal to 400° C., the residence time of         said feedstock in the conversion unit is comprised between 5 and         70 minutes; and/or     -   when the target temperature of said feedstock is greater than         400° C., the residence time of said feedstock in the conversion         unit is comprised between 1 and 10 minutes;         b) a fractionation of said hydrocarbon-containing feedstock is         carried out in a fractionation unit in order to produce a top         effluent comprising elemental mercury;         c) the top effluent obtained in stage b) is brought into contact         with a mercury capture material contained in a unit for the         capture of mercury, in order to obtain an effluent that is at         least partially de-mercurized.

Advantageously, the reduction in the total content by weight of mercury of said feedstock taken before stage a) and after stage c) is at least 90%.

According to the invention, stages a) and b) are carried out simultaneously.

In an embodiment according to the invention, the top effluent originating from the fractionation of said feedstock in the main fractionation unit is cooled by means of a heat exchanger so as to produce a liquid effluent. Advantageously, the liquid effluent is sent to a separation unit in order to provide a liquid organic phase a part of which is recycled to the main fractionation unit by way of reflux, and the other part is sent via the pipe to said unit for the capture of mercury.

In another embodiment according to the invention, the top effluent originating from the fractionation of said feedstock in the main fractionation unit is heated by means of a heat exchanger so as to produce a gaseous effluent. Advantageously, the gaseous effluent is compressed using a compressor before being sent to the unit for the capture of mercury.

Preferably, before stage a) of transformation of the non-elemental mercury contained in the compounds of said feedstock to elemental mercury, said feedstock is desalted in a desalting unit.

In an embodiment according to the invention, during stage c), said feedstock is brought into contact with a bulk or supported mercury capture material comprising a phase containing at least one metallic sulphide based on a metal M selected from the group constituted by copper, chromium, manganese, iron, cobalt and nickel.

In another embodiment according to the invention, during stage c), said feedstock is brought into contact with a bulk or supported capture material comprising a phase containing at least sulphur in elemental form.

Preferably, said hydrocarbon-containing feedstock comprises between 1 and 10 mg of mercury per kg of feedstock, preferentially 1 to 1200 μg/kg, more preferentially 10 to 500 μg/kg.

Advantageously, the heavy hydrocarbon-containing feedstock is a crude oil feedstock.

DESCRIPTION OF THE FIGURES

FIG. 1 diagrammatically shows a conventional fractionation process for a heavy hydrocarbon-containing feedstock, and more particularly a crude oil feedstock. In the interests of clarity, the equipment provided (pumps, valves, heat exchangers etc) is not necessarily shown.

FIG. 2 diagrammatically shows an embodiment of the process according to the invention in which the single capture unit is situated downstream of the main fractionation unit.

FIG. 3 shows an embodiment according to the invention for which the mercury capture stage is carried out in liquid phase.

FIG. 4 shows an embodiment according to the invention for which the mercury capture stage is carried out in gas phase.

DETAILED DESCRIPTION OF THE INVENTION

For better understanding of the invention, the description given hereinafter by way of an example application relates to a process for the elimination of heavy metals, and more particularly mercury, in a heavy hydrocarbon-containing crude oil feedstock. Of course, the process according to the invention can be used for the elimination of other heavy metals, such as arsenic, lead, vanadium and cadmium, contained in a heavy hydrocarbon-containing feedstock.

Within the meaning of the present invention, by heavy hydrocarbon-containing feedstock is meant, a feedstock having a density at 15° C. greater than approximately 750 kg/m³, composed essentially of hydrocarbons, but also containing other chemical compounds which, apart from the carbon and hydrogen atoms, have heteroatoms, such as oxygen, nitrogen, sulphur and heavy metals such as mercury, arsenic, lead, vanadium or cadmium. Preferably, said hydrocarbon-containing feedstock comprises between 1 and 10 mg of mercury per kg of feedstock, preferentially 1 to 1200 μg/kg, more preferentially 10 to 500 μg/kg.

By non-elemental mercury is meant any form of mercury other than in the elemental (or atomic) form, i.e. in the molecular form, and/or in the ionic form, and/or in complexed forms.

The description of FIG. 1 relates to a conventional process for the elimination of heavy metals contained in a crude oil feedstock; the description of FIGS. 2 to 4 relates to a process for the elimination of heavy metals according to the invention. FIGS. 2 to 4 repeat certain elements of FIG. 1; the references in FIGS. 2 to 4 that are identical to those in FIG. 1 denote the same elements.

Process According to the Prior Art (FIG. 1)

FIG. 1 diagrammatically shows the first treatments undergone by a heavy hydrocarbon-containing, and more particularly a crude oil, feedstock with a view to its initial fractionation, generally carried out by atmospheric distillation. Typically, a heavy hydrocarbon-containing, and more particularly a crude oil, feedstock is sent via the pipe 100 into a desalting unit 1000, consisting generally of washing with water. The main function of this stage is to eliminate the majority of the soluble inorganic species contained in said feedstock. The desalted feedstock is then sent via the pipe 101 into a pre-heating unit 2000. The purpose of this stage of heating the desalted feedstock is to bring said feedstock to a temperature close to the temperature of the bottom of the fractionation unit 3000 situated downstream of the pre-heating unit 2000. The pre-heating temperature is generally comprised between 200 and 400° C., and depends on the number of distillation columns used in the main fractionation unit 3000. The pre-heated feedstock is then sent via the pipe 104 to the main fractionation unit 3000.

The main fractionation unit 3000 can comprise one or more distillation columns (in FIG. 1, a single distillation column is shown). The main fractionation unit 3000 makes it possible to produce different hydrocarbon cuts depending on their molecular weights and more particularly depending on their difference in volatility. For example, the fractionation of the feedstock by atmospheric distillation associated with the distillation columns of the main fractionation unit allows the separation of the feedstock into different cuts, from the lightest to the heaviest, and more particularly into fuel gases (C1, C2), propane (C3), butane (C4), light gasoline (C5 to C6), heavy gasoline (C7 to C10), kerosene (C10 to C13), gas-oil (C13 to C20/25), or also atmospheric residue (C20/C25+).

At the outlet of the main fractionation unit 3000, the top effluent of the main fractionation unit generally contains hydrocarbon-containing compounds of which 90% of said compounds have a boiling point less than 200° C. at atmospheric pressure (1.01325×10⁵ Pa). The top effluent is sent via the pipe 400 to a secondary fractionation unit 4000 comprising one or more fractionation columns, allowing the production of different hydrocarbon cuts. Generally, at the output of the secondary fractionation unit 4000 various hydrocarbon-containing compounds can be distinguished, such as:

-   -   fuel gases evacuated through the pipe 401 comprising a majority         of hydrocarbon-containing species with one or two carbon atoms         (C1/C2) as well as purification effluents, such as H₂ or H₂S. In         the interests of clarity, a single flow of fuel gases has been         shown in FIG. 1, but this number can vary in an industrial site         according to the choice of the operator;     -   liquid petroleum gas (LPG) evacuated through the pipe 402         comprising a majority of hydrocarbon-containing species with         three or four carbon atoms (C3/C4);     -   the naphtha cuts evacuated through the pipe 403 comprising a         majority of the hydrocarbon compounds with 5 carbon atoms or         more (C5+), the upper limit of the number of carbon atoms         depending on the choice of the cut point utilized at the top of         the main fractionation unit 3000. Furthermore, according to the         fractionation layout selected by the operator, there may be         several naphtha cuts (not shown in the Figure) for example a         heavy naphtha cut and a light naphtha cut.

The hydrocarbon-containing cuts evacuated via the pipes 401, 402 and 403 are generally each treated by a unit for the capture of heavy metals in elemental form, and more particularly the capture of mercury in elemental form. As shown in FIG. 1, the capture units 5001, 5002, 5003 are generally placed downstream of the main fractionation unit 3000, in the direction of circulation of the feedstock, for each of the hydrocarbon-containing cuts circulating in the pipes 401, 402 and 403. The capture units 5001, 5002 and 5003 each comprise a mercury capture material in the form of a fixed bed. The mercury capture materials can be all those known to a person skilled in the art for the capture of elemental mercury. The de-mercurized hydrocarbon-containing cuts are evacuated through the pipes 411, 412 and 413 respectively.

Therefore, because of the presence of a multiplicity of hydrocarbon-containing cuts in such a process, the number of capture units comprising the capture materials becomes significant (a specific capture unit is associated with each cut of hydrocarbon-containing compounds originating from the fractionation unit 4000), especially as the number of capture units is generally doubled in order to be able to regenerate the capture materials without interrupting the operation of the unit.

Furthermore, in such a process layout, different types of capture material are used in order to treat on the one hand, the gaseous flows, for example evacuated through the pipe 401, and on the other hand the liquid flows, for example evacuated through the pipe 403, but also the flows that may contain hydrogen, such as certain fuel gases, requiring specifically adapted capture materials.

The Applicant discovered, surprisingly, that it is possible to eliminate the heavy metals, and more particularly the non-elemental mercury, contained in the compounds of a hydrocarbon-containing feedstock, and more particularly a crude oil feedstock, by carrying out a stage of transforming the non-elemental mercury contained in the compounds of said feedstock to elemental mercury, and a stage of capturing the elemental mercury; said stage of transformation of the non-elemental mercury contained in the compounds of said feedstock being carried out by a heat treatment of said feedstock at a target temperature during a residence time sufficient to allow the transformation of the non-elemental mercury contained in the compounds of said feedstock to elemental mercury, even without the use of any catalytic or hydrogen treatment. The process according to the invention thus comprises a single unit for the capture of elemental mercury and so comprises a single capture material.

In fact, although the crude oil feedstocks comprise a very great diversity of hydrocarbon-containing molecules, bringing said feedstock up to a temperature during a sufficient residence time makes it possible to transform the non-elemental mercury contained in the compounds of the feedstock to elemental mercury, it then being possible to capture the latter with a single capture material.

More particularly, the process according to the invention comprises:

a) a stage of transformation of the non-elemental mercury contained in the compounds of the heavy hydrocarbon-containing feedstock, and more particularly in a crude oil feedstock, to elemental mercury; b) a stage of fractionation of said hydrocarbon-containing feedstock by a main fractionation unit. c) a stage of capture of the mercury in elemental form recovered at the top of said main fractionation unit by means of a unit for the capture of mercury comprising a capture material.

According to the invention, stages a) and b) can be carried out separately or simultaneously.

Therefore it is possible to collect the mercury contained in the top effluent of the main fractionation unit by using a suitable unit for the capture of mercury, thus making it possible to dispense with the capture units generally positioned on the different flows of light compounds situated in the main fractionation unit in a conventional refinery layout.

Process According to the Invention (FIGS. 2 to 4)

With reference to FIG. 2, showing a simplified illustration of the process according to the invention, a heavy hydrocarbon-containing feedstock is sent via the pipe 100 into a desalting unit 1000. The desalted feedstock is then sent via the pipe 101 into a unit 200 for the conversion of the non-elemental mercury contained in the compounds of the heavy hydrocarbon-containing feedstock to elemental mercury.

Within the context of the present invention, the conversion unit 200 corresponds:

-   -   according to one embodiment to the heating unit 2000, such as a         drum, and optionally with a pipe or a set of pipes intended for         the transport of said feedstock to the main fractionation unit         3000. In this embodiment, stages a) and b) of the process         according to the invention are carried out separately, i.e. the         transformation of the mercury to elemental mercury is carried         out upstream of the main fractionation unit 3000; or     -   according to another embodiment with the heating unit 2000, such         as a drum, and optionally with a pipe or a set of pipes intended         for the transport of said feedstock to the main fractionation         unit 3000, and to the main fractionation unit 3000. In this         embodiment, stages a) and b) of the process according to the         invention are carried out simultaneously, i.e. the         transformation of the mercury to elemental mercury is carried         out both during the transport of said feedstock to the main         fractionation unit 3000 and during the stage of fractionation of         said feedstock in the main fractionation unit 3000.

According to the invention, by main fractionation unit 3000 is meant a unit for the fractionation of the feedstock by atmospheric distillation (such as described previously in the section describing the prior art). The main fractionation unit 3000 can comprise one or more distillation columns. The main fractionation unit 3000 makes it possible to produce different hydrocarbon cuts depending on their molecular weight and more particularly depending on their difference in volatility.

When the conversion unit 200 comprises a drum, said drum advantageously comprises a double wall covering the drum wherein a heat transfer fluid circulates in order to maintain the temperature of said feedstock at the target temperature up to the main fractionation unit 3000, or advantageously comprises a resistive heater inserted directly inside said drum.

When the conversion unit 200 comprises a pipe or a set of pipes, the pipe or set of pipes advantageously comprise a double jacket in which a heat transfer fluid circulates in order to maintain the temperature of said feedstock at the target temperature up to the main fractionation unit 3000.

a) Stage of Transformation of the Non-Elemental Mercury Contained in the Compounds of the Heavy Hydrocarbon-Containing Feedstock to Elemental Mercury

Stage a) of transformation of the non-elemental mercury contained in the compounds of the heavy hydrocarbon-containing feedstock to elemental mercury is essential according to the invention, as it makes it possible to maximize the transformation of the non-elemental mercury to elemental mercury. In fact, regardless of the nature and/or the origin of the heavy hydrocarbon-containing feedstock, the latter can comprise mercury in different forms. For example, mercury may be found in the form of elemental or atomic mercury (also called Hg^(o)) and/or in organic molecular form, and/or in ionic form, for example in the form of Hg²⁺ and complexes thereof.

According to the invention, the transformation of the non-elemental mercury contained in the compounds of the feedstock to elemental mercury is carried out via a conversion unit 200.

Therefore, according to the invention, the process for the transformation of the non-elemental mercury contained in the compounds of said feedstock to elemental mercury comprises passing said feedstock, at a temperature determined by a person skilled in the art, into a conversion unit 200 during a residence time fixed so that at least 90% by weight, preferably at least 95% by weight, and even more preferentially at least 99% by weight of the non-elemental mercury contained in the compounds of said feedstock are converted to elemental mercury, even in the absence of a catalyst.

Therefore, depending on the temperature of the feedstock, the residence time necessary in order to carry out the transformation of the non-elemental mercury contained in the compounds of said feedstock to elemental mercury corresponds to the following equation (1):

$\begin{matrix} {{\ln\left( \frac{{- \ln}\frac{C_{s}}{C_{0}}}{t} \right)} = {{\ln \left( k_{0} \right)} - \frac{E_{a}}{RT}}} & (1) \end{matrix}$

in which: C_(s) corresponds to the concentration of mercury (apart from elemental mercury) contained in the compounds of said feedstock at the outlet of the conversion unit 200 (in mol·L⁻¹); C_(o) corresponds to the concentration of mercury (apart from elemental mercury) contained in the compounds of said feedstock at the inlet of the conversion unit 200 (in mol·L⁻¹); t corresponds to the residence time (in seconds); k₀ corresponds to the constant of the rate of transformation of non-elemental mercury to elemental mercury (in seconds⁻¹); E_(a) corresponds to the activation energy of the reaction for the transformation of non-elemental mercury to elemental mercury (in J·mol⁻¹); R corresponds to the ideal gas constant (R=8.314 J·K⁻¹·mol⁻¹); T corresponds to the temperature of the feedstock (in K).

In the embodiment for which stages a) and b) are carried out separately, i.e. the transformation of mercury to elemental mercury is carried out upstream of the main fractionation unit 3000, the concentration C_(s) corresponds to the mercury concentration (apart from elemental mercury) measured in the line 102 at the inlet of the main fractionation unit 3000, and the concentration C_(o) corresponds to the mercury concentration (apart from elemental mercury) measured in the line 101.

In the embodiment for which stages a) and b) are carried out simultaneously, i.e. the transformation of mercury to elemental mercury is carried out both during the transport of said feedstock to the main fractionation unit 3000 and during the stage of separation of said feedstock in the main fractionation unit 3000, the concentration C_(s) corresponds to the mercury concentration (apart from elemental mercury) measured in the line 400, and the concentration C_(o) corresponds to the mercury concentration (apart from elemental mercury) measured in the line 101.

Furthermore, according to the invention, the total volume V of the conversion unit 200 is defined such that the ratio V/Q, with Q corresponding to the volume flow of the feedstock to be treated, is equal to the residence time “t” associated with the targeted temperature of the feedstock “T”.

Thus, in the embodiment for which stages a) and b) are carried out separately, i.e. when the transformation of mercury to elemental mercury is carried out upstream of the main fractionation unit 3000, the volume V of the conversion unit 200 corresponds to the volume of the heating unit 2000, such as a drum, and optionally to the pipe or the set of pipes intended for the transport of the feedstock to the main fractionation unit 3000.

In the embodiment for which stages a) and b) are carried out simultaneously, i.e. when the transformation of mercury to elemental mercury is carried out both during the transport of said feedstock to the main fractionation unit 3000 and during the stage of separation of said feedstock in the main fractionation unit 3000, the volume V of the conversion unit 200 corresponds to the volume of the heating unit 2000, such as a drum, and optionally to the volume of the pipe or the set of pipes intended for the transport of the feedstock to the main fractionation unit 3000, as well as to the volume of the main fractionation unit 3000, in which unit the transformation of the non-elemental mercury contained in the compounds of the heavy hydrocarbon-containing feedstock to elemental mercury is also carried out.

With reference to FIG. 2, the volume V of the conversion unit 200 corresponds to the cumulative volume of the heating unit 2000, the pipe 102 and the volume of the main fractionation unit 3000.

Advantageously, during the transformation stage, and according to any one of the embodiments according to the invention (i.e. stages a) and b) being carried out separately or not):

-   -   when the target temperature of said feedstock is comprised         between 150° C. and 175° C., the residence time of said         feedstock in the conversion unit 200 is comprised between 150         and 2700 minutes; and/or     -   when the target temperature of said feedstock is greater than         175° C. and less than or equal to 250° C., the residence time of         said feedstock in the conversion unit 200 is comprised between         100 and 900 minutes; and/or     -   when the target temperature of said feedstock is greater than         250° C. and less than or equal to 400° C., the residence time of         said feedstock in the conversion unit 200 is comprised between 5         and 70 minutes; and/or     -   when the target temperature of said feedstock is greater than         400° C., the residence time of said feedstock in the conversion         unit 200 is comprised between 1 and 10 minutes;

Even more preferably:

-   -   when the target temperature of said feedstock is comprised         between 150° C. and 175° C., the residence time of said         feedstock in the conversion unit 200 is comprised between 150         and 2700 minutes; and/or     -   when the target temperature of said feedstock is greater than         175° C. and less than or equal to 200° C., the residence time of         said feedstock in the conversion unit 200 is comprised between         100 and 900 minutes; and/or     -   when the target temperature of said feedstock is greater than         200° C. and less than or equal to 225° C., the residence time of         said feedstock in the conversion unit 200 is comprised between         30 and 300 minutes; and/or     -   when the target temperature of said feedstock is greater than         225° C. and less than or equal to 250° C., the residence time of         said feedstock in the conversion unit 200 is comprised between         15 and 150 minutes; and/or     -   when the target temperature of said feedstock is greater than         250° C. and less than or equal to 300° C., the residence time of         said feedstock in the conversion unit 200 is comprised between 5         and 70 minutes; and/or     -   when the target temperature of said feedstock is greater than         300° C. and less than or equal to 400° C., the residence time of         said feedstock in the conversion unit 200 is comprised between 1         and 40 minutes; and/or     -   when the target temperature of said feedstock is greater than         400° C. and less than or equal to 500° C., the residence time of         said feedstock in the conversion unit 200 is comprised between 1         and 10 minutes; and/or     -   when the target temperature of said feedstock is greater than         500° C., the residence time of said feedstock in the conversion         unit 200 is comprised between 1 and 5 minutes.

According to the invention, the stage of transformation of the non-elemental mercury contained in the compounds of the feedstock to elemental mercury is carried out at a pressure comprised between 0.1 and 12 MPa, preferably between 0.1 and 6 MPa. Thus it is possible to transform the non-elemental mercury contained in the compounds of the heavy hydrocarbon-containing feedstock, and more particularly of crude oil feedstock, to elemental mercury, starting from 150° C., by adjusting the residence time of the feedstock in the conversion unit 200. Furthermore, the absence of a catalyst simplifies the implementation of the process and makes it possible to avoid clogging the heavy metals capture materials in the subsequent stage or stages by the deposition of gums, the precursors of which are produced (for example by cracking of the hydrocarbon-containing molecules) by contact with a mercury capture material.

b) Fractionation Stage

According to the invention, a stage of fractionation of the feedstock is carried out in a main fractionation unit 3000. The main fractionation unit 3000 can comprise one or more distillation columns (in FIG. 2, a single distillation column is shown). The main fractionation unit 3000 makes it possible to produce different hydrocarbon cuts depending on their molecular weights and more particularly depending on their difference in volatility. For example, the fractionation of the feedstock by atmospheric distillation associated with the distillation columns of the main fractionation unit allows the separation of the feedstock into different cuts, from the lightest to the heaviest, and more particularly into fuel gases (C1, C2), propane (C3), butane (C4), light gasoline (C5 to C6), heavy gasoline (C7 to C10), kerosene (C10 to C13), gas-oil (C13 to C20/25), or also atmospheric residue (C20/C25+).

The mercury in elemental form and the most volatile hydrocarbon-containing compounds are recovered via the pipe 400 in the top effluent of the main fractionation unit.

The top effluent 400 from the main fractionation unit generally contains hydrocarbon-containing compounds of which 90% of said compounds have a boiling point less than 200° C. at atmospheric pressure (1.01325×10⁵ Pa).

Furthermore, the top effluent 400 comprises at least 90% by weight of elemental mercury with respect to the total weight of the mercury present in the initial feedstock, preferentially at least 95% by weight and even more preferentially at least 99% by weight.

c) Stage of Capture of the Elemental Mercury

The top effluent 400 from the main fractionation unit 3000, comprising mercury in elemental form, is then sent to a unit for the capture of mercury 5000 comprising a capture material capable of reacting with the elemental mercury in order to trap it in the bed so as to produce an effluent 420 that is at least partially de-mercurized. The unit for the capture of mercury 5000 can also contain means for adjusting the pressure and the temperature (not shown in FIG. 2) in order to be adapted to the selected method for the elimination of mercury.

More specifically, the capture material utilized in the capture unit 5000 is selected from those known to a person skilled in the art. The capture material is preferably in the form of a bed composed of elemental particles which can be in any form known to a person skilled in the art. The latter can for example be in the form of balls, single- or multi-lobed cylinders, preferably with a number of lobes comprised between 2 and 5 or in the form of rings.

The capture material contains a compound, usually called active phase, which reacts with the heavy metal so as to capture the heavy metal on the capture material.

For mercury, the active phase of the capture material can comprise metals which, in their sulphurized form, react with mercury. The metallic sulphide or sulphides contained in the capture material according to the invention are based on a metal selected from the group constituted by copper (Cu), chromium (Cr), manganese (Mn), iron (Fe) cobalt (Co) and nickel (Ni). Preferably, the metal or metals of the metallic sulphide or sulphides are selected from the group constituted by copper (Cu), manganese (Mn), iron (Fe) and nickel (Ni). Very preferably, if a single metallic sulphide is present, copper sulphide is chosen.

Alternatively, the active phase used can also be elemental sulphur as described in patent document FR 2 529 802.

Preferably, the capture material can be constituted by an active phase, as described above, distributed over a porous support.

The porous support can preferably be selected from aluminas, phosphorus-containing aluminas, silica-aluminas, silicas, clays, activated carbons, zeolites, titanium oxides, zirconium oxides, silicon carbide and mixtures thereof.

A capture material containing a support and copper sulphide is for example described in the document U.S. Pat. No. 4,094,777.

The capture material can be obtained by any means of preparation known to a person skilled in the art, such as for example impregnation, co-mixing or co-granulation.

Bringing the effluent to be treated into contact with the capture material can be carried out at a temperature comprised between −50° C. and 1550° C., preferentially between 0° C. and 1120° C., and more preferentially between 20° C. and 100° C. Moreover, it can be carried out at an absolute pressure comprised between 0.01 MPa (0.1 bar) and 20 MPa (200 bars), preferentially between 0.1 MPa (1 bar) and 15 MPa (150 bars), and more preferentially between 0.1 MPa (1 bar) and 12 MPa (120 bars).

In addition, this stage of bringing the effluent to be treated into contact with the capture material can be carried out with an H.S.V. (Hourly Space Velocity of the gaseous or liquid effluent) comprised between 0.1 h⁻¹ et 50000 h⁻¹. The unit for hourly space velocity being expressed in litres of gaseous or liquid effluent per hour per litre of catalyst (L/h/L), i.e. h-1). For a gaseous effluent to be treated, the H.S.V. can preferentially be comprised between 50 h⁻¹ and 500 h⁻¹.

The contact with the capture material advantageously makes it possible to capture the heavy metals, in particular mercury, contained in the effluent to be treated, and to obtain an effluent having a content of heavy metals, in particular mercury, that is reduced with respect to the content in the initial effluent, or even to eliminate the heavy metals entirely from the effluent.

Advantageously, the reduction in the total content by weight of mercury, between the gaseous or liquid effluent before treatment and the effluent obtained after treatment with the capture material can represent at least 90%, preferentially at least 95%, and more preferentially at least 99%.

FIG. 3 represents a detailed layout of stage c) the capture of mercury according to the invention when the latter is carried out in liquid phase. This configuration is particularly suitable for recovering the elemental mercury in condensed phase. The top effluent recovered via the pipe 400 originating from the main fractionation unit 3000 is cooled via a heat exchanger 6000 so as to condense it. The condensed top effluent recovered via the pipe 430 is then brought to a main separation unit 7000. The separation unit 7000 can be a drum. The separation unit 7000 can optionally comprise a separation of the condensed aqueous phases evacuated via the pipe 500. A part of the condensed organic phase 431 is pressurized, for example using a pump 8000, in order to be recycled via the pipe 432 to the main fractionation unit 3000 by way of reflux. The remaining part recovered via the pipe 433 is optionally pressurized, for example by using a pump 8001, in order to be sent via the pipe 434 to a capture unit 5000 comprising a capture material for heavy metals, and more particularly a capture material for mercury. An at least partially de-mercurized liquid flow thus results, that is recovered via the pipe 420.

FIG. 4 shows a detailed layout of stage c) of mercury capture according to the invention when the latter is carried out in gas phase.

The top effluent recovered via the pipe 400 originating from the main fractionation unit 3000 is optionally heated via the heat exchanger 6001 so as to create a superheated gaseous effluent 435. This optional stage may prove useful for avoiding the phenomena of capillary condensation that may appear in the capture materials for heavy metals. Optionally, the superheated effluent can be pressurized, for example using a compressor 9000. The purpose of this pressurizing stage is, if necessary, to compensate for the pressure drop caused by the capture unit 5000. The top effluent, optionally superheated and/or optionally compressed is sent via the pipe 436 to the capture unit 5000 comprising a capture material for heavy metals, and more particularly a capture material for mercury. A gaseous hydrocarbon phase thus results that is at least partially de-mercurized and is recovered via the pipe 420.

d) Additional Treatment Stage

At the outlet of the unit for the capture of mercury 5000, the at least partially de-mercurized effluent is sent via the pipe 420 to a treatment unit 4000 such as described above (cf. the paragraph relating to the process according to the prior art). As a result, there are a plurality of effluents 411, 412 and 413 is at the outlet of the treatment zone 4000, that do not comprise mercury, and thus have no need to be treated through units for the capture of mercury.

Thus, unlike the state of the art shown in FIG. 1, the method according to the invention requires only one single unit for the capture of mercury, it being possible optionally to double said capture unit in parallel or in series in order to provide for maintenance without impacting on the operation of the fractionation unit. Moreover, the process according to the invention makes it possible to recover the mercury contained in the compounds of the feedstock, and more particularly in the crude oil feedstock, immediately at the outlet of a main fractionation unit in a refinery layout. Within the meaning of the invention, by refinery is meant the set of operations that make it possible to transform crude oil to petroleum products in current use. The crude oils are in the form of liquids that are more or less viscous essentially constituted by hydrocarbons of varying volatility and chemical composition.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding French application No. 15/57.033, filed Jul. 24, 2015, are incorporated by reference herein.

Example

The example refers to FIGS. 2 and 3.

In this example, it is assumed that the conversion unit 200 is composed of the heating unit 2000, the pipe 102 and the main fractionation unit 3000.

A crude oil feedstock 100 is sent into a desalting unit 1000 consisting of washing with water. The desalted feedstock 101 is heated via the heat exchanger 2000 to a target temperature of 380° C. and is then conveyed via the pipe 102 to the main fractionation unit 3000 composed of a distillation column so as to produce different hydrocarbon cuts, depending on their molecular weights. The contact time (residence time) of the feedstock in the conversion unit 200 is 10 minutes.

At the outlet of the main fractionation unit 3000, the top effluent 400 is composed of a hydrocarbon cut 90% of the compounds of which have a boiling point less than 200° C. The top effluent 400, after cooling to 46° C. via a heat exchanger 6000, is treated by a capture unit 5000 comprising a mercury capture material based on CuS deposited on an alumina, capable of capturing mercury in elemental form. As a result, an at least partially de-mercurized effluent 420 produced is sent to a treatment unit 4000 that is in the form of a secondary fractionation unit. Three effluents 411, 412 and 413 are extracted at the outlet of the treatment zone 4000.

The different feedstocks and effluents 100, 101, 102, 400 and 420 were analyzed in order to determine their mercury content. The analysis of the total mercury in the liquid and gaseous fractions was carried out respectively using a specific PE-1000® device for mercury analyses and a SP-3D® device from Nippon Instruments Corporation (NIC). The total mercury content in the pipes 101, 102, 102, 400 and 420 was determined in μg/L.

For the chemical speciation of mercury, the method applied is as described in the scientific publication by Charles-Philippe Lienemann et al. published in the journal Fuel Processing Technology, 131, 2015, pages 254-261, entitled: “Mercury speciation in liquid petroleum products: Comparison between on-site approach and lab measurement using size exclusion chromatography with high resolution inductively coupled plasma mass spectrometric detection (SEC-ICP-HR MS)” and comprising the following stages:

-   -   filtration in order to eliminate the particulate mercury;     -   purging the filtrate in order to eliminate the volatile         elemental mercury;     -   extraction with cysteine of the purged filtrate: separation of         the extractable ionic mercury and organic non-extractable         mercury (analysis of the aqueous solution using DMA-80         (Milestone Inc)).

The results obtained are presented in Table 1 below.

TABLE 1 Mercury concentrations and compositions % by weight % by weight % by [Hg]total particulate Hg⁰ weight ionic % by weight Pipes (μg/L) Hg (elemental) Hg organic Hg 100 182 63 0 5 32 101 124 82 7 2 9 102 127 79 12 1 8 400 117 0 100 0 0 420 2 0 0 40 60

Implementation of the process according to the invention makes it possible on the one hand, to efficiently convert the non-elemental mercury contained in the compounds of the crude oil feedstock to elemental mercury. It is noted on the one hand that the majority of the transformation of the non-elemental mercury to elemental mercury takes place in the main fractionation unit 3000. In fact, 12% by weight of the mercury in elemental form is found in the pipe 102, i.e. at the inlet of the main fractionation unit 3000, and in the pipe 400, 100% by weight of mercury in elemental form is found i.e. at the outlet of the overhead stream from the main fractionation unit 3000. On the other hand, the process according to the invention makes it possible to capture the elemental mercury efficiently at the outlet of the main fractionation unit 3000 via the unit for the capture of mercury 5000 situated between the pipes 400 and 420, which makes it possible to avoid polluting all of the units situated downstream of the main fractionation unit of the crude oil feedstock in a refinery layout.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. Process for the elimination of mercury contained in a heavy hydrocarbon-containing feedstock downstream of a main fractionation unit (3000), a process in which: a) the non-elemental mercury contained in the compounds of said feedstock is transformed to elemental mercury, said stage being carried out in a conversion unit (200) at a target temperature during a fixed residence time and adapted to said target temperature so that at least 90% by weight of non-elemental mercury contained in the compounds of said feedstock is converted to elemental mercury, said transformation stage being carried out in the absence of hydrogen and in the absence of a catalyst, it being understood that: when the target temperature of said feedstock is comprised between 150° C. and 175° C., the residence time of said feedstock in the conversion unit (200) is comprised between 150 and 2700 minutes; and/or when the target temperature of said feedstock is greater than 175° C. and less than or equal to 250° C., the residence time of said feedstock in the conversion unit (200) is comprised between 100 and 900 minutes; and/or when the target temperature of said feedstock is greater than 250° C. and less than or equal to 400° C., the residence time of said feedstock in the conversion unit (200) is comprised between 5 and 70 minutes; and/or when the target temperature of said feedstock is greater than 400° C., the residence time of said feedstock in the conversion unit (200) is comprised between 1 and 10 minutes; b) a fractionation of said hydrocarbon-containing feedstock is carried out in a fractionation unit (3000) in order to produce a top effluent (400) comprising elemental mercury; c) the top effluent (400) obtained in stage b) is brought into contact with a mercury capture material contained in a unit for the capture of mercury (5000), in order to obtain an effluent that is at least partially de-mercurized (420).
 2. Process according to claim 1, characterized in that the reduction in the total content by weight of mercury of said feedstock taken before stage a) and after stage c) is at least 90%.
 3. Process according to claim 1, characterized in that stages a) and b) are carried out simultaneously.
 4. Process according to claim 1, characterized in that the top effluent (400) originating from the fractionation of said feedstock in the main fractionation unit (3000) is cooled by means of a heat exchanger (6000) so as to produce a liquid effluent (430).
 5. Process according to claim 4, characterized in that the liquid effluent (430) is sent into a separation unit (7000) in order to provide a liquid organic phase a part of which is recycled to the main fractionation unit (3000) by way of reflux, and the other part is sent via the pipe (434) to said unit for the capture of mercury (5000).
 6. Process according to claim 1, characterized in that the top effluent (400) originating from the fractionation of said feedstock in the main fractionation unit (3000) is heated by means of a heat exchanger (6001) so as to produce a gaseous effluent (435).
 7. Process according to claim 6, characterized in that the gaseous effluent (435) is compressed by means of a compressor (9000) before being sent to the unit for the capture of mercury (5000).
 8. Process according to claim 1, characterized in that before stage a) of transformation of the non-elemental mercury contained in the compounds of said feedstock to elemental mercury, said feedstock is desalted in a desalting unit (1000).
 9. Process according to claim 1, characterized in that during stage c), said feedstock is brought into contact with a bulk or supported mercury capture material comprising a phase containing at least one metallic sulphide based on a metal M selected from the group constituted by copper, chromium, manganese, iron, cobalt and nickel.
 10. Process according to claim 1, characterized in that during stage c), said feedstock is brought into contact with a bulk or supported mercury capture material comprising a phase containing at least sulphur in elemental form.
 11. Process according to claim 1, characterized in that said hydrocarbon-containing feedstock comprises between 1 and 10 mg of mercury per kg of feedstock.
 12. Process according to claim 1, characterized in that the heavy hydrocarbon-containing feedstock is a crude oil feedstock. 